1. Field of the Invention
The present invention relates to an electromagnetically operated electric switch, for example a contactor, comprising an operating magnet, the armature of which, upon operation of the switch, performs a translatory movement. The armature is connected to the movable contact assembly of the electric switch in such a way that the contact assembly moves in the same direction as the armature between a closed and an open position.
2. Prior Art
Normally, the contact assemblies of large contactors are designed with a movable main contact and one or more fixed main contacts in each phase. To reduce the risk of contact welding and increase the life of the contacts, the contacts are normally provided with contact elements of some silver alloy, for example silver cadmium oxide. Silver alloys are expensive materials, and the cost of said contact elements constitutes a not insignificant part of the price of a contactor. It is therefore desirable to reduce the required amount of silver.
In prior art contactors, it has been proposed to use separate movable main contacts and arcing contacts with separate spring systems (see e.g. German Auslegeschrift No. 1 237 667 and French patent specification No. 1 431 326). In such a design, the arcing contacts make and break the main current, whereas the main contact for the most part carries the current in closed position. A drawback in connection with the proposed contactors with double contacts is, however, that they require a relatively great operating power for the closing operation, since prior art contactors of this kind are provided with helical type opening springs, which are disposed in the direction of movement of the magnet armature. These springs are arranged to influence directly a contact carrier, fixed to the magnet armature, with a returning force acting against the attractive force of the magnet. Upon closing of such a contactor, the opening springs are compressed, the counter force from the springs thus increasing with reduced magnet air gap. Since the operating magnet at the final stage of the closing must also overcome the counter force from the contact pressure springs, it is necessary to use, in such a design, a relatively strong operating magnet. This has an adverse effect on the dimensions, price and power consumption of the contactor.
It is also known (for example, from German Auslegeschrift No. 1 140 263 and U.S. patent specification No. 3,873,952), in a contactor with a conventional contact system, to arrange its opening springs in such a way that the returning force emanating from the springs is reduced upon closing.